Heretofore, the oscillating forward and backward motion is applied to the fabric at the binding or beat-up point in a rhythm 1:1 superimposed on the normal woven web withdrawal motion equivalent to that of a linen binding characteristic of the seersucker fabric. The motion application is such that the effect or pile warp threads undergo a length addition in comparison to the base warp threads. The device is connected to a drive branched off from the main drive train of the loom.
Conventional devices used heretofore achieve the necessary differential motion between the base warp thread gang and the effect and pile warp thread gang in such a manner that the length addition was obtained through the naturally occurring differing tensions (tension difference between the effect or pile warp thread gang and the base warp thread gang). Conventionally, these different tensions are achieved by a different drive of the pile warp beam compared to the base warp beam of the loom. In this manner, the intended length addition for the effect or pile warp threads can only be achieved more or less randomly. Thus, in this context it is only possible to adjust the length addition within a relatively large scatter range. Heretofore, during the beat-up of the weft thread the effect or pile warp threads adjusted for a somewhat easier movement, were carried along more than the base warp threads, whereby the desired length addition is achieved. However, this length addition is only reproducible within a large scatter range so that the woven fabric produced by such a known device is in itself very nonuniform, especially when a large length addition was called for. With these known devices, length additions up to approximately 30 to 32% can be achieved.